The therapeutic implications of angiogenic growth factors were first described by Folkman and colleagues over two decades ago (Folkman, N Engl J Med, 285:1182-1186 (1971)). Recent investigations have established the feasibility of using recombinant angiogenic growth factors, such as fibroblast growth factor (FGF) family (Yanagisawa-Miwa, et al., Science, 257:1401-1403 (1992) and Baffour, et al., J Vasc Surg, 16:181-91 (1992)), endothelial cell growth factor (ECGF)(Pu, et al., J Surg Res, 54:575-83 (1993)), and more recently, vascular endothelial growth factor (VEGF) to expedite and/or augment collateral artery development in animal models of myocardial and hindlimb ischemia (Takeshita, et al., Circulation, 90:228-234 (1994) and Takeshita, et al., J Clin Invest, 93:662-70 (1994)). In studies with recombinant angiogenic growth factors, intra-muscular administration of the growth factor was repeated over a range of 10 to 14 days. Thus, one major limitation of recombinant protein therapy is its potential requirement to maintain an optimally high and local concentration over time.
Gene delivery systems employed to date have been characterized by two principal components: a macro delivery device designed to deliver the DNA/carrier mixture to the appropriate segment of the vessel, and microdelivery vehicles, such as liposomes, utilized to promote transmembrane entry of DNA into the cells of the arterial wall. Macrodelivery has typically been achieved using one of two catheters initially developed for local drug delivery: a double-balloon catheter, intended to localize a serum-free arterial segment into which the carrier/DNA mixture can be injected, or a porous-balloon catheter, designed to inject gene solutions into the arterial wall under pressure. Jorgensen et al., Lancet 1:1106-1108 (1989); Wolinsky, et al., J. Am. Coll. Cardiol., 15:475-485 (1990); March et al., Cardio Intervention, 2:11-26 (1992)); WO93/00051 and WO93/00052.
Double balloon catheters are catheters which have balloons which, when inflated within an artery, leave a space between the balloons. The prior efforts have involved infusing DNA-containing material between the balloons, allowing the DNA material to sit for a period of time to allow transfer to the cells, and then deflating the balloons, allowing the remaining genetic material to flush down the artery. Perforated balloons are balloons which have small holes in them, typically formed by lasers. In use, fluid containing the genetic material is expelled through the holes in the balloons and into contact with the endothelial cells in the artery. These gene delivery systems however, have been compromised by issues relating to efficacy and/or safety.
Certain liabilities, however, inherent in the use of double-balloon and porous balloon catheters have been identified. For example, neither double-balloon nor porous balloon catheters can be used to perform the angioplasty itself. Thus, in those applications requiring both angioplasty and drug delivery, e.g., to inhibit restenosis, two procedures must be preformed. Additionally, the double balloon typically requires long incubation times of 20-30 min., while the high-velocity jets responsible for transmural drug delivery from the porous balloon catheter have been associated with arterial perforation and/or extensive inflammatory infiltration (Wolinsky, et al., supra).
Recently, the feasibility of intra-arterial gene therapy for treatment of ischemia was demonstrated in a rabbit model with VEGF using another gene delivery system, a Hydrogel-coated angioplasty balloon. Successful transfer and sustained expression of the VEGF gene in the vessel wall subsequently augmented neovascularization in the ischemic limb (Takeshita, et al., Proc Natl Acad Sci USA (In Press)). However, alternative methods for inducing angiogenesis are still desirable for a number of reasons. First, use of catheter based gene delivery systems may bring out unpredictable abrupt closure or severe damage at the site of ballooning. The consequence may be more serious if the damaged artery is the major donor of the present collaterals or the only patent vessel supplying ischemic tissue. Second, it may be difficult to deliver a catheter to the distal lesion especially in cases of diffuse vascular disease. Finally, despite major advances in both surgical and percutaneous revascularization techniques, limb salvage and relief of ischemic pain cannot be achieved in many patients with diffuse peripheral vascular disease. Isner et al., Circulation 88:1534-1557 (1993)).
Striated animal muscle has been shown to take up and express injected foreign marker genes transferred in the form of plasmid DNA (Wolff, et al., Science, 247:1465-1468 (1990)). Therapeutic gene transfection in the form of naked plasmid DNA injected directly into muscles has advantages over techniques using viral vectors and catheter based delivery systems. Mainly, it is free from immunological reactions associated with viral proteins (Miller, Nature, 357:455-60 (1992)), and avoids possible vascular injuries due to catheter delivery or ballooning procedures. However, direct gene transfer is considered to have insufficient expression to be considered for use in human gene therapy trials (Wolff, et al., supra, and Jiao, et al., Hum Gene Ther, 3:21-33 (1992)).